The present invention relates to an active vehicle stability control system and method using electronically controlled limited-slip differentials to enhance vehicle lateral dynamics while preserving longitudinal motion.
Anti-lock braking systems (ABS) have become an integral part of modern passenger vehicles and may be used to improve vehicle traction and stability. Typical traction control systems based on brake intervention have the disadvantage of dissipating an amount of energy roughly equal to that spent in biasing the high-friction wheel. For example, when a vehicle attempts to accelerate or climb on a split-friction (split-μ), low-high friction surface, it often loses its energy to the braking system by dissipating the same amount of energy it biases to the high-friction wheel. Hence, the braking torque limits the driving torque on the high-friction wheel and is often insufficient to move the vehicle, such as in an uphill-driving situation.
To overcome this limitation, traction control using electronically controlled limited-slip differentials (ELSDs) may be applied at the driven wheels so that the vehicle can maintain longitudinal motion by sending more traction torque to the higher friction wheel. Fully locked differentials achieve the best possible longitudinal traction but, on slippery or split-μ surfaces, the lateral dynamics of the vehicle may be degraded and deviate from the driver's intended direction. Indeed, the bias traction torque must be properly controlled to prevent undesired yaw motion and eventual degradation of the lateral dynamics of the vehicle.
At relatively high speeds, yaw stability control systems may be applied to prevent the vehicle from losing control. Most vehicle stability control systems in the market are brake-based. Brake-based stability control systems use ABS hardware to apply individual wheel braking forces in order to correct vehicle yaw dynamics. However, brake-based systems suffer from the limitation that the speed performance of vehicle is deteriorated and conflicts with the driver's actions. To overcome the brake-based stability control limitation, the use of active torque distribution stability control would be more beneficial under acceleration close to the vehicle's stability limit.
The last two decades have witnessed significant growth in the application of four-wheel-drive (4WD) systems to passenger vehicles. Limited-slip differential (LSD) technology is already being used in many production models. ELSDs are widely used and available in the automotive market, and are known to have the capability of adding yaw damping to the vehicle in addition to their superior traction performance.